The present invention relates to an electric charge image recording medium and a recording/reproducing apparatus.
FIG. 1 is a block diagram which shows an example of the composition of a recording/reproducing apparatus based on electric charge image. Referring to this FIG. 1, D represents an electric charge recording medium disk (hereinafter, described only as Medium D) comprising a laminar structure of a charge retention layer member IL and an electrode E. The electric charge retention layer member IL is composed of the material of such an extremely high insulation resistance that electric charges adhering on the member IL can be maintained for a long time (for example, a silicon resin). The charge retention layer member IL can also be comprised of any other configuration.
This Medium D is rotated at a predetermined revolution frequency by a rotary driving mechanism not illustrated. Referring to FIG. 1, WA represents a recording system configured so as to be capable to emit an electromagnetic radiation ray flux the intention of which is modulated by a recording object information signal (in the following description, the electromagnetic radiation ray flux is mentioned like a laser light flux while describing a source of generating electromagnetic radiation rays like a laser light source) from a lens 7. The recording system WA in the illustrated example comprises a laser light source 1, a lens 2, a polarizer 3, an optical modulator 4, a recording object information signal source 5, an analyzer 6 and a lens 7. Symbol RA in FIG. 1 is a reproducing system constructed in such a manner that an information signal recorded in the Medium D in the form of electric charges is read by a laser light flux and output as an electric signal. In the example shown in FIG. 1, the reproducing system comprises a laser light source 2, lenses 9, 12 and 15, a polarizer 10, a beam splitter 11, a wave plate 13, an analyzer 14, a photoelectric converter 16, an amplifier 17, an output terminal 18, etc.
A laser light flux emitted from the lens 7 of the recording system WA is transmitted through a transparent electrode Etw of a recording head WH comprising a laminar structure of the transparent electrode Etw and a photoconductive layer PCE, and applied to the photoconductive layer PCE. A voltage from a power source Vw across the transparent electrode Etw of the recording head WH and the electrode E of the Medium D. Therefore, when an intensity-modulated laser light flux enters the photoconductive layer PCE of the recording head WH according to an information signal sent from the recording system WA, the electric resistance at a portion of the photoconductive layer PCE to which the laser light flux was given decreases while activating to a charge retention layer member IL of the Medium D in the portion, thereby depositing electric charges on the surface of the charge retention layer member IL in the Medium D, according to the information signal. An image of electric charges created according to the information signal is regenerated as follows by the reproducing system. It is assumed that a detection head comprises a dielectric mirror DML, an optical modulation member layer PML, consisting of a single crystal of, for example, lithium niobate and a transparent electrode Etr. The optical modulation member layer PML changes the plane of polarization of light transmitted in the layer by an electric field created by the image of electric charges adhering on the surface of a charge retention layer member IL in the Medium D. Meanwhile, a laser light flux emitted from a lens 12 in the reproducing system RA is transmitted through the optical modulation member layer PML, reflected by the dielectric mirror DML and then entered in the lens 12 again. The plane of polarization of the light reflected above is changed according to the image of electric charges on the surface of the charge retention layer member in the Medium D.
The light entered again in the lens 12 in the above of which the plane of polarization has been changed according to the image of electric charges adhering on the surface of the charge retention layer member IL in the Medium D is supplied to an analyzer 14 via a beam splitter 11 and a wave plate 13. Thus, the analyzer 14 emits the light of a light quantity which changes according to the variation of the plane of polarization of the entered light. The output light is collected by a lens 15, given to a photoelectric converter 16 where it is converted to an electric signal. The output signal from the photoelectric converter 16 is amplified in an amplifier 17 thereby an output terminal 18 in the reproducing system issues the original information signal.
In the meantime, with the recording/reproducing apparatus based on the electric charge image, information stored in an electric charge image recording medium in a high recording density can be reproduced and recorded again easily using a simple device, by using the laser light of a satisfactorily small diameter. However, in order to reproduce a data recorded in a high recording density in terms of fidelity, it is necessary to drive and displace a reproducing element under a tracking control process. For this purpose, the applicant corporation of the present invention already proposed a reproducing device illustrated in FIG. 2.
FIG. 2 shows the block diagram of an already proposed electric charge image type reproducing device where a tracking control system applies to the reproducing element in a system of reproducing recorded image of electric charges. FIG. 3 is the block diagram of the tracking control system. Referring to FIG. 2, a Medium D comprises a laminar structure of a charge retention layer member IL and an electrode E, like with an already described Medium D. The Medium D is rotated by a rotary driving mechanism not illustrated, at a predetermined revolution frequency. The WA shown in FIG. 2 is configured in the same manner as the already described recording system WA referring to FIG. 1; namely it is a recording system comprising a laser light source 1, a lens 2, a polarizer 3, an optical modulator 4, a recording object information signal source 5, an analyzer 6 and a lens 7. The aspect of recording information by means of the recording system WA shown in FIG. 2 is the same as that already described referring to FIG. 1.
The RA in FIG. 2 is a reproducing system that reads information signal recorded in the Medium D in the image of electric charges, using a laser light while outputting as electric signals. Its partial configuration comprising a laser light source 2, lenses 9, 12 and 15, a polarizer 10, a beam splitter 11, a wave plate 13 and an analyzer 14 is the same as that of the reproducing system already described referring to FIG. 1. However, according to the aspect of the configuration shown in FIG. 2, the component parts of the photoelectric converter 16, amplifier 17 and the output terminal 18 in the reproducing system of FIG. 1 have been modified to a split type photodetector PD, tracking control circuit TSC, actuator ACT, etc. provided with photoelectric converter elements PDa-PDd.
Referring to FIG. 3, among output signals Sa-Sd from four photoelectric conversion elements PDa-PDd constituting the split type photodetector PD, output signals Sa and Sc from the elements PDa and PDc, respectively, are added by an adder 19 in the tracking control signal generating circuit TSC. In addition, among output signals Sa-Sd from four photoelectric conversion elements PDa-PDd constituting the split type photodetector PD, output signals Sb and Sd from the photoelectric conversion elements PDa-PDd, respectively, are added by an adder 20 in the tracking control signal generating circuit TSC.
Output signals (Sa+Sc) and (Sb+Sd) from the adders 19 and 20 respectively, are added by an adder 21 from which a reproduced signal of (Sa+Sb+Sc+Sd) is transmitted to an output terminal 18.
In addition, output signals (Sa+Sc) and (Sb+Sd) from the adders 19 and 20, respectively, are operated for {(Sa+Sc)-(Sb+Sd)} in a subtractor 22, while the phase of an output signal from the subtractor 22 being compensated in a phase compensation circuit PC thereby becoming a tracking control signal which is supplied to an actuator ACT from an output terminal 23. The actuator ACT drives and displaces the reproducing element in the direction orthogonal to the extension of a recorded track for the purpose of tracking control.
With the reproducing device based on the electric charge image, as already proposed and shown in FIG. 2, a tracking control signal is generated according to a reproduced signal obtained by reproducing an information signal recorded on the surface of the charge retention layer member IL of the Medium D as an image of electric charges, and supplied to the actuator. The actuator drives and displaces the reproducing element in the direction orthogonal to the extension of a recorded track. However, there is also another proposal of generating tracking control information according to the change of the geometrical shape of the charge recording medium in order to have more preferable tracking control processing.